Global warming: Andes glacier melt to affect water supplies

New study tracks rapidly accelerating rate of ice decline since 1950s

The Perito Moreno Glacier is one of the largest in Patagonia at 30 kilometers long. The glacier descends from the Southern Patagonian Icefield (image top)—2100 meters elevation (6825 feet) in the Andes Mountains—down into the water and warmer altitudes of Lago Argentino at 180 meters above sea level. Satellite image courtesy NASA Earth Observatory.

By Summit Voice

SUMMIT COUNTY — Glaciers in large parts of the Andes have shrunk on average by 30 to 50 percent since the 1970s, and the unprecedented retreat could soon begin to affect water supplies for Andean communities.

Globally, glaciers have been retreating at a moderate pace as the planet warmed after the peak of the Little Ice Age, a cold period lasting from the 16th to the mid-19th century. Over the past few decades, however, the rate of melting has increased steeply in the tropical Andes, at a pace not seen for at least the last 300 years.

The melting is more pronounced for small glaciers at low altitudes, the authors said. Glaciers at altitudes below 5,400 metres have lost about 1.35 meters in ice thickness (an average of 1.2 meters of water equivalent per year since the late 1970s, twice the rate of the larger, high-altitude glaciers.

“Because the maximum thickness of these small, low-altitude glaciers rarely exceeds 40 metres, with such an annual loss they will probably completely disappear within the coming decades,” Rabatel said.

The researchers also reported that the amount of rainfall in the region did not change much over the past few decades and, therefore, cannot account for changes in glacier retreat. Instead, climate change is to blame for the melting: regional temperatures increased an average of 0.15°C per decade over the 1950-1994 period.

“Our study is important in the run-up to the next IPCC report, coming out in 2013,” said Rabatel. The Intergovernmental Panel on Climate Change has pointed out that tropical glaciers are key indicators of recent climate change as they are particularly sensitive to temperature changes. The tropical Andes host 99 percent of all tropical glaciers in the world, most of them in Peru.

The research is also important to anticipate the future behavior of Andean glaciers and the impact of their accelerated melting on the region.

“The ongoing recession of Andean glaciers will become increasingly problematic for regions depending on water resources supplied by glaciated mountain catchments, particularly in Peru,” the scientists wrote.

Without changes in precipitation, the region could face water shortages in the future.

The Santa River valley in Peru will be most affected, as its hundreds of thousands of inhabitants heavily rely on glacier water for agriculture, domestic consumption, and hydropower. Large cities, such as La Paz in Bolivia, could also face shortages.

“Glaciers provide about 15 percent of the La Paz water supply throughout the year, increasing to about 27 percent during the dry season,” said Alvaro Soruco, a Bolivian researcher who took part in the study.

In their comprehensive review of Andean glaciers, the scientists synthesized data collected over several decades, some dating as far back as the 1940s.

“The methods we used to monitor glacier changes in this region include field observations of glacier mass balance, and remote-sensing measurements based on aerial photographs and satellite images for glacier surface and volume changes,” Rabatel explained.

The study takes into account data collected for glaciers in Colombia, Ecuador, Peru and Bolivia, covering a total of almost a thousand square kilometers. This corresponds to about 50 percent of the total area covered by glaciers in the tropical Andes in the early 2000s.

The research was conducted to provide the scientific community with a comprehensive overview of the status of glaciers in the tropical Andes and determine the rate of retreat and identify potential causes for the melting. But the authors hope the results can have a wider impact.

“This study has been conducted with scientific motivations, but if the insight it provides can motivate political decisions to mitigate anthropogenic impact on climate and glacier retreat, it will be an important step forward,” Rabatel concluded.